This invention relates to a substrate inspection system which provides a visual inspection device to the last or an intermediate one of a plurality of processes that are sequentially carried out for the production of component-mounting substrates for inspecting the substrate by image processing after the corresponding process has been carried out.
Component-mounting substrates (hereinafter referred to simply as substrates) are generally produced by a method including a process of printing a cream solder on a printed circuit board by means of a solder printer using a silk screen method (hereinafter referred to as the solder printing process), a process of using a mounter to mount components onto this substrate with the cream solder printed thereon (hereinafter referred to as the component mounting process) and a process of soldering these mounted components to the substrate by carrying the component-mounted substrate into a reflow oven and heating it (hereinafter referred to as the reflow process).
On a production line for substrates adapted to carry out this series of processes, it is preferable to provide a visual inspection device to each of the processes for carrying out an inspection by using an image processing method on the substrate on which the corresponding process has been carried out.
On the premise of carrying out an inspection after each of the production processes as explained above, the assignee of this invention has earlier developed a system having a data processor with a computer as its main component connected to the inspection device associated with each process. As described in Japanese Patent Publication Tokkai 2004-361145, this system is formed such that each inspection device transmits the image used for its inspection to the data processor and that the data processor displays the images of the same portion of the same substrate after the processes together on a same image screen. Such a system is capable of comparing the images of the substrate after the different processes regarding a portion with a defect, determining the process in which the abnormality causing the defect has occurred and carrying out an analysis for identifying the cause of the defect from the result of such determination. Thus, imperfections in the production line can be determined quickly and accurately.
If a large number of substrates are produced by this production line and parts of the devices used in the processes become worn, the quality of the produced substrates may become adversely affected. If the mask of the printer used in the solder printing process becomes clogged, for example, the area of the printed part corresponding to the clogged portion may become smaller or deformed. If the force of the suction pad on the mounter becomes weaker, as another example, the component mounted by such a pad may fail to be mounted correctly and become displaced.
Such adverse effects on the quality of the produced substrate due to worn-out conditions of device parts are likely to occur continuously. Moreover, the lowering of quality of this type tends to progress with time, finally reaching the level of being a defect.
If an inspection device is provided to each of the processes, the lowering of the product quality and its causes can be detected relatively easily by making judgments by providing these inspection devices not only with reference values for judging a defect but also with reference values for determining the degree of lowered product quality. If a system described in aforementioned Japanese Patent Publication is introduced, furthermore, the cause of lowered product quality can be accurately determined because the images of substrates earlier inspected can be individually compared for each process.
A user without a sufficient capital, however, may opt to provide an inspection device only for the reflow process at the end of the line, or at most for the component mounting process and the reflow process. With such a system, it may be possible to detect the existence of a portion with lowered quality but it is difficult to correctly identify its cause.
Consider a situation where an inspection device is provided only to the reflow process. A component which is somewhat displaced may be detected by such an inspection device but it is difficult to determine whether this displacement was caused at the time of mounting components or during the reflow process.